Thin-layer chromatographic separation of serotonin from epinephrine and norepinephrine

A thin-layer chromatographic procedure is reported for the separation of serotonin from epinephrine and norepinephrine. The method involves the use of ethylenediaminetetraacetic acid-impregnated silica gel G plates and n-butanol-ethanol-acetic acid-water (8:2:1:3) as developer. Serotonin is well separated from both epinephrine and norepinephrine. Epinephrine and norepinephrine overlapped slightly but were both detectable. The procedure is thus applicable to the separation of all three biogenic amines in spite of the absence of an absolutely clear separation of epinephrine from norepinephrine.     

Heats of solution and neutralization ofLewis acids and bases in acetic anhydride

Heats solution of someLewis acids and bases in acetic anhydride have been determined and the following order of their relative strengths is proposed: SbCl₅>SO₃>SnCl₄>TiCl₄>AsCl₃ and piperidine> n-butylamine>potassium acetate>sodium acetate -picoline>quinoline. Heats neutralization of theseLewis acids and bases in acetic anhydride suggest that the major enthalpy change in these neutralization reactions is due to the combination of a proton and the (CH₂COOCOCH₃)-ion, resulting in the formation of acetic anhydride.

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Lösungs- und Neutralisationswärmen von Lewis-Säuren und-Basen in Essigsäureanhydrid

Zusammenfassung Es wurden die Lösungswärmen einigerLewis-Säuren in Essigsäureanhydrid bestimmt und folgende Reihung nach ihrer relativen Stärke vorgeschlagen: SbCl₅>SO₃>SnCl₄>TiCl₄>AsCl₃ und Piperidin> n-Butylamin>KAc>NaAc-Picolin>Chinolin. Die Neutralisationswärmen dieserLewis-Säuren und-Basen legen nahe, daß der Hauptanteil daran auf die Reaktion eines Protons mit (CH₂–COOCOCH₃)-zurückzuführen ist.

     

Homoatomic P --> P coordination: a versatile synthetic approach to polyphosphorus dications

Polyphosphorus dications have been synthesised and comprehensively characterised as diphosphine (dppe, dmpe and dpph) linked Ar2P+ Lewis acids (Ar = C6H5); this application of unique homoatomic coordination chemistry provides important building blocks for extended systems.     

Competing reaction pathways from α-halo-α-protioalkyl aryl sulfoxides initiated by organometallic reagents

The reactions of syn-1-haloethyl p-chlorophenyl sulfoxides (halogen = Cl, Br) with main-group organometallic reagents (n-BuMgCl, MeLi, n-BuLi, s-BuLi, and t-BuLi) in THF and PhMe solvents were examined. Product distributions were analyzed to determine the extent of competing sulfoxide ligand exchange, halogen-metal exchange, and deprotonation reaction pathways. A combination of t-BuLi in PhMe was optimal for initiation of sulfoxide ligand exchange from syn-1-chloroethyl p-chlorophenyl sulfoxide.     

The Raman active internal vibrational modes of potassium nitrate

The Raman active internal vibrational modes of single crystal orthorhombic potassium nitrate have been studied in various polarizations. The full multiplet structure predicted by factor group analysis for the v₂ and v₃ regions has been observed for the first time. The expected site group splitting of the v₄ mode was not observed and can be assumed to be less than 0.5 cm^?1.     

Validity of the Hammond postulate and constraints on general one-dimensional reaction barriers

The Hammond postulate is a useful, qualitative tool that interrelates structural similarities between reactants, transition structures, and products with the exo- or endothermicity of reactions. It applies to most chemical reactions, although several exceptions are known. In this study the following problem is addressed: is it possible to formulate conditions for the validity of the quantitative Hammond postulate in terms of simple physical quantities characteristic to the molecules involved? A detailed analysis is given for the conditions of validity of the postulate, in terms of bounds on the internal forces and force constants of nuclear arrangements encountered along a reaction path. We have determined a broad class of constraints on barrier shapes that must be satisfied in order to obtain a critical situation that violates the Hammond postulate: a reactant-like transition structure (“transition state”) for endothermic reactions, and a product-like one for exothermic reactions. The general constraints are formulated in terms of physically meaningful quantities: (i) energy differences, (ii) restrictions on slopes (e.g., an upper bound on internal forces), and (iii) restrictions on curvatures (e.g., upper bounds on force constants) along potential curves.     

Rhodium(II)-Catalyzed CH Insertions with {[(4-Nitrophenyl)sulfonyl]imino}phenyl-λ3-iodane

The [Rh₂(OAc)₄]-catalyzed decomposition of {[(4-nitrophenyl)sulfonyl]imino}phenyl-λ³-iodane (NsN?IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O-substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron-releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral Rh^II catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh-complexed nitrene into the CH bond is proposed.     

Forward and backward pericyclic photochemical reactions have intermediates in common, yet cyclobutenes break the rules.

Photochemical pericyclic reactions are believed to proceed via a so-called pericyclic minimum on the lowest excited potential surface (S(1)), which is common to both the forward and backward reactions. Such a common intermediate has never been directly detected. The photointerconversion of 1,3-butadiene and cyclobutene is the prevailing prototype for such reactions, yet only diene ring closure proceeds with the stereospecificity that the Woodward-Hoffmann rules predict. This contrast seems to exclude a common intermediate. Using ultrafast spectroscopy, we show that the excited states of two cyclobutene/diene isomeric pairs are linked by not one, but by two common minima, p* and ct*. Starting from the diene side (cyclohepta-1,3-diene and cycloocta-1,3-diene), electrocyclic ring closure passes via the pericyclic minimum p*, whereas ct* is mainly responsible for cis-trans isomerization. Starting from the corresponding cyclobutenes (bicyclo[3.2.0]heptene-6 and bicyclo[4.2.0]octene-7), the forbidden isomer is formed from ct*. The path branches at the first (S(2)/S(1)) conical intersection towards p* and ct*. The fact that the energetically unfavorable ct* path can compete is ascribed to a dynamic effect: the momentum in C=C twist direction, acquired--such as in other olefins--in the Franck-Condon region of the cyclobutenes.     

Metallacycloalkanes: I. Preparation and characterisation of α,α′-bipyridyl-5-nickela-3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane

Oxidative addition of 2 molecules of 3,3-dimethylcyclopropene (I) to α,α′-bipyridyl(1,5-cyclooctadiene)nickel(0) (III) gave the title compound (IV) in over 90% yield. Complex IV was characterized by mass, ¹H NMR and ¹³C NMR spectroscopy. Its structure was determined by X-ray diffraction (a 13.7081(2), b 14.638(2), c 9.5139(1) Å, β 110.82(1)°, C2/c, R = 0.05 for 1614 reflections).